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Nanostructuration by self-organization of block copolymers

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Morphology control by exposure to solvent vapors

A film formed after depositing a solution of a block copolymer exhibits an ill-defined morphology due to the rapid evaporation of the solvent, which freezes the system into a metastable state. Exposure to solvent vapors allows the film to reorganize into ordered morphologies that depend on exposure time and the nature of the solvent. We perform in situ and ex situ studies to better describe these structural reorganizations.

General diagram of the process of solvent vapor annealing (SVA) : surface topography of polystyrene-block-poly lactic acid thin films after (initial) deposition and after exposure to solvent vapors.

Visualization of the modification of the internal structure of a thin film of poly (isoprene-block-styrene-block- (2-vinylpyridine)) upon exposure to solvent vapors. The transformation mechanism (gyroid  cylinder) involves an unprecedented phase transition, induced by the thin film configuration.

Achievement of unconventional morphologies

The behavior of complex systems (such as star block copolymers, triblocks or mixtures of blocks copolymers) is investigated to produce unconventional morphologies. Morphologies resulting from the formation of an interface with a non-constant radius of curvature can be obtained, for example, by means of blends of block copolymers having different block sizes.

Examples of unconventional morphologies obtained for blends of triblock terpolymer, namely poly (isoprene-block-styrene-block- (2-vinylpyridine))

Fabrication of porous films and porosity infiltration

The selective degradation of the minority domains offers the possibility to form nano-porous films, which can contribute to a better description of the internal topology of the formed films (ellipso-porosimetry, replication of the porosity by infiltration of inorganic precursors). This is based on the use of selectively degradable blocks. We also use the porosity infiltration process for the fabrication of arrays of nanoobjects, or nano-devices for nanofluidic.

Examples of replication (SEM images, bottom) of various porosity topologies (AFM images, inset)

Example of realization of a microfluidic device obtained by inorganic replication of a film having a cylindrical porosity, perpendicular to the surface of the film.

Fabrication of nanoparticle arrays

The selective inclusion of inorganic precursors in the domains allows the realization of networks of organized nanoparticles. The presence of patterns of controlled geometry, topology and organization, in size ranges today reaching only a few nanometers, makes it possible to envision the use of these systems as a realistic alternative to current optical lithography processes. The use of copolymers with small, highly incompatible blocks allows sizes <10nm to be achieved.

Interaction of films with pulsed lasers

The interaction of a pulsed laser (femto or pico second) with a surface allows for its structuration at the scale close to the wavelength of the laser used. This phenomenon known as laser-induced periodic surface structures (LIPSS) can be exploited in thin films of block copolymers to guide their self-organization.

Examples of pulsed laser-induced surface nanostructures (LIPSS) for various types of homopolymers (program APR-IA COMEMAT, Région Centre-Val de Loire, GREMI)